The 1995 Nobel Prize in Chemistry was shared by Paul Crutzen, F. Sherwood Rowlan

Question

The 1995 Nobel Prize in Chemistry was shared by Paul Crutzen, F. Sherwood Rowland. and Mario Molina for their work concerning the formation and decomposition of ozone in the stratosphere. Rowland and Molina hypothesized that chlorofluorocarbons (CFCs) in the stratosphere break down upon exposure to UV radiation, producing chlorine atoms. Chlorine was previously identified as a catalyst in the breakdown of ozone into oxygen gas. Using the enthalpy of reaction for two reactions with ozone, determine the enthalpy of reaction for the reaction of chlorine with ozone.

Explanation / Answer

ANSWER:

CONCEPT:

In order to solve such a problem we have to subtract/add the given reactins in such a way so that the net result will be the reacion of our concern as explained. If we subtract reation 1 from reaction 3 we will get reaction 3(The reaction of our concern)

subtract (1) reaction from (2) reaction

Cl(g) + 2O2 (g) ------------> ClO(g) + O3(g) H = 122.8KJ (HINT: When we subtract a reaction from other we simply revrse it and change the sign of H)

2O3(g) ---------------> 3O2(g)   H = -285.3KJ

So the net reaction

Cl(g) + O3 (g) ------------> ClO(g) + O2(g)

H = H1 - H2

H = -285.3 - (-122.8) = -162.5KJ

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